Gauge Manifolds are Obsolete

Gauge manifolds are quickly becoming obsolete. There are now at least four alternatives that allow you to check system pressures and temperatures without connecting a manifold set. Why is this important? Every time you connect a set of manifold gauges, you lose refrigerant. A standard ¼” hose holds around 1/3 of an ounce per foot when filled with liquid. That means a six foot hose will hold around 2 ounces when connected to a liquid line. So assuming the system was charged perfectly when you arrived, after connecting your manifold gauges, it is now under charged.

So how are you going to check systems pressures, superheat, and subcooling without connecting a gauge manifold? You connect a gauge, just not a gauge manifold. Sporlan, Appion, Yellow Jacket, and Testo all make small digital gauges designed to connect directly to the system with no intermediate hoses. These all lose far less refrigerant than even one foot of hose. They also all offer ways of checking the suction and liquid line temperatures. Typically through wireless clamp-on temperature probes. They all offer Bluetooth connectivity, allowing software to calculate superheat and subcooling, perform data logging, and system analysis. Since the software is downloaded to your phone or tablet, updates for new refrigerants are no problem.

One caveat – except for the Appion gauges, they all require a phone or tablet to display their readings. The Appion gauges do have their own digital display, but the others all rely on the portable display you carry around with you all the time.

What about evacuation and charging? The Yellow Jacket Mantooth has a port built in for that, the others will all require an adapter – such as a valve core tool. However, if you are pulling vacuums and your time means anything, you should have valve core tools anyway. You can connect a valve core tool to the system, connect the digital gauge to the side port, and charge through the back port on the valve core tool.

How does all this make gauge manifolds obsolete?
First, you don’t need a manifold to check system pressures and temperatures, in fact, it is better to use the small direct connect gauges for that.

Second, you don’t need a gauge manifold to pull a vacuum: two valve core tools, two large bore hoses, a vacuum gauge, and a vacuum pump with at least two hose connections are what you need for that.

Finally, you don’t need a gauge manifold to charge a system. One valve core tool, two short digital gauges, two temperature clamps, and one hose will allow you to charge a system while checking both pressures, the superheat, and the subcooling. What you will also need is a phone, tablet, or laptop that is rugged enough to be used day I and day out and can be easily recharged.  

Mini-Split, Multi-Split, and VRF Systems

Unless you have been living under a rock, you are sure to have noticed the rise of mini-split, multi-split, and variable refrigerant flow systems. This segment of the HVAC market has spawned a whole new vocabulary. The discussions about this equipment and even the technical literature are replete with this new jargon. So I thought I would spend a few moments to discuss some of the more common terms.

Unitary
This is not a new term, but you may often hear traditional systems referred to as unitary. Really, this just means that the system is a manufactured unit, instead of a field built system. However, it is often used to designate traditional HVAC systems: split systems as well as packaged units.

Mini-Split Systems
Mini-split systems are indeed split systems, with an outdoor condensing unit and an indoor blower-coil, which is often referred to as a head. Some common heads are high wall mount, ceiling mount, floor mount, and compact cassette – which tucks away above the finished ceiling. As the name mini-split implies, both the outdoor and indoor units are much smaller than found in traditional unitary systems.  For the most part, the indoor units are designed to be mounted in the space they are conditioning, with no ductwork. For this reason, many people also refer to mini-split systems as ductless systems. However, mini-split systems are actually available with both low static and high static ducted indoor heads which are designed to be installed in a concealed area. Static refers to the static air pressure  difference the blower is designed operate against while moving the air. Low static units are designed for very short, single runs – not complete duct systems. High static indoor units are designed to be used with complete duct systems. They are used more in commercial applications than residential applications.

Multi-Split Systems
Multi-split units are designed to be used with multiple indoor heads. The idea is to install one outdoor unit to supply from two to four indoor units. On typical multi-split units, the refrigerant line sets for all heads run back to the outdoor unit. The outdoor unit has connections for up to four indoor units. Another type of system which is often referred to as multi-split uses a small refrigerant network for up to nine heads. This type of system has one line set with branches that wye off at each indoor unit. These are really more like a small variable refrigerant flow (VRF) system.

Variable Refrigerant Flow
The term variable refrigerant flow (VRF) has two uses within the industry. The more global definition simply refers to any system which varies the flow or refrigerant to match the load. This is usually accomplished by changing the compressor speed. Truthfully, most mini-split and multi-split systems fit the global definition of variable refrigerant flow. There are now several unitary systems which incorporate variable refrigerant flow. Most of these systems use variable speed compressors to match the compressor capacity and refrigerant flow to the load.

However, variable refrigerant flow (VRF) also has a more specific meaning which refers to a specific type of system. These VRF systems distribute refrigerant via a network of refrigerant piping that supplies multiple indoor heads. Heating and cooling is distributed using refrigerant lines instead of ductwork.

One of the difficulties in studying this segment of the industry is the lack of uniform terms. For example, Daikin refers to their VRF system as  VRV for variable refrigerant volume. Each manufacturer tends to have their own name for the different network components. The components used to branch off from the main refrigerant line to feed an individual head have several names, depending on the manufacturer. They are called refnet joints (Daikin), branch joints (Mitsubishi), separation tubes (Fujitsu), or Y-branch fittings (LG). Most manufacturers have boxes that take a single refrigerant flow and divide it up among several heads. Common names include branch selectors (Daikin), branch controllers (Toshiba), branch boxes (Mitsubishi), flow selectors (Toshiba), or heat recovery units (LG).

Heat Recovery Systems
Again, the term heat recovery has several meanings within the field. The global definition simply refers to any system which finds a productive use for the condenser heat, such as heating hot water, or dehumidification reheat. In the VRF world, heat recovery systems refer specifically to a VRF system which can heat and cool simultaneously. This is accomplished by moving heat from rooms which need to be cooled to rooms which need to be heated. This way the heat is recovered and reused, rather than being discarded.

Hopefully this discussion will help you make sense of the mini-multi jargon. For more details, refer to Unit 46 Mini-Split, Multi-Split, and VRF Systems in Fundamentals of HVACR, 3rd edition.

Belt Basics

Belts are seldom used today in residential applications, but they are common in commercial applications. Understanding a few belt basics can make the commercial technician’s life much easier. The main type of belt used in HVACR is the V-belt, named for the V cross-section shape. The sides of the belt that form the V are what should be riding on the pulley, not the bottom of the belt. Belts are made of layers of cords encased inside rubber, similar to car tires. The cords provide strength.

Belt Identification
There are two predominant naming conventions for HVACR belts. One uses 3L, 4L, and 5L to designate belt widths of approximately 3/8”, 1/2”, and 5/8”. A number follows the with designation which gives the belt circumference in inches. So a 5L-440 is approximately 5/8” in width and 44 inches in circumference. The other common convention is A, B, and C for 1/2”, 5/8”, and 7/8” widths respectively.

Matched Belts
Large commercial applications may use multiple belts on the same drive. You should always ask for a matched set – not just two or three of the same size. This is because there can be small differences in length, which are of no consequence when using one belt. However, when using several on the same sheaves, they must be identical or some of the belts will be loose. A matched set is much closer to identical than just two belts with the same name size. This also means you should always replace all of the belts, even if only one of them needs replacing.

Installing a Belt
A common (and incorrect) way to install a belt is to roll it over the edge of the pulley. This saves time, but damages the cords in the belt – leading to shortened life. The correct way is to loosen the belt tensioner or motor mount so that the belt fits easily over the motor and fan pulleys. Then tension the belt using the belt tensioner or by adjusting the motor, depending on the design.

How Tight Should it Be
Many techs make the belt as tight as they possibly can get it. However, a belt only needs to be tight enough so that it does not slip at maximum torque. For fan belts, that is at start-up. Belt tension is measured by pressing in the middle of the belt while measuring both the force used and the amount of belt deflection. Browning recommends a deflection of 1/64 the belt span. The span is the center to center distance between the pulleys. So a belt with a 64" span should have a 1" deflection. The amount of force varies with the particular belt and span. Browning publishes a chart for their belts. A belt tension gauge is used to measure the deflection force. There are a couple of different ones out there. Again, Browning makes one.

Curing Belt Jitters
Many techs mistake misaligned belts as being loose. A belt that vibrates and jumps up and down usually indicates alignment issues. Remember that the shafts and pulleys must be aligned in three dimensions. The shafts should be parallel to each other. If you extend an imaginary line out from the shafts they should not intersect each other. You should be able to lay a straight edge across the pulley faces. If one pulley is farther forward than the other the belt will jump.

Worn Belts
Worn belts typically have shiny, glazed sides. If you see this, replace the belt. The hard, slick sides can’t grab the pulley wall, and so it slips even if the belt is correctly tensioned.

Belt Lubrication
Belts do NOT NEED to be lubricated. An old trick is to spray some WD-40 on a slipping and squealing belt to quiet it down. This basically just makes it slip quietly – just long enough for you to leave. It does not fix the problem. If anything, it makes the belt slip worse. It also does not last very long and leads to early belt failure.